Most multifamily housing units are either heated from a central source such as a central boiler or are heated from one or more sources in each dwelling unit. In the latter case, the heat source may consist of a gas or oil furnace, an electric heat pump, or electric resistance heating units. Currently, most multifamily dwelling units are air-conditioned, either from a central chilled water source, by individual through-the-wall or window air conditioners, or by the use of an individual heat/cool heat pump within each dwelling unit. Domestic hot water is commonly supplied from a central source, although in some cases each dwelling unit will have an individual electric or gas water heater.
Experience has shown that when the tenant pays for the utilities, there is a significant reduction in energy consumption. For this reason, and in order to shield themselves from energy rate increases that they cannot pass off to the tenants, many building owners would prefer that tenants pay for their own utilities. While this may be reasonably straightforward in the case of electricity, it is not so straightforward in the case of gas heat and hot water. In buildings with central boilers, there are technical and legal obstacles to metering and charging tenants for the hot water they use. The problems associated with venting flue products and the space requirements of separate furnaces and gas water heaters makes individual space and water heating impractical for many dwelling units. Although many dwelling units have individual electric submetering, and while individual electric air conditioning is a viable option, electric heating via heat pumps or resistance heating is more expensive than gas heating in most areas of the country.
Space requirements are extremely important in multi-family housing. The typical multifamily dwelling unit is significantly smaller than a single-family dwelling unit. From the developer's standpoint, a high value is placed on usable space, so appliances which require a minimum of floor space may command a premium.
Therefore, a need exists for an integrated appliance which combines space heating and cooling and potable water heating in a single compact package, and which provides these functions with a minimum operating cost. With current technologies and energy costs, the most economical method of providing these functions is to utilize electric air conditioning and gas space heating and potable water heating.